Many mothers-to-be happily pay for a keepsake that is essentially a fetal ultrasound, never wondering about the ultrasound’s safety. After all, they receive ultrasounds at their obstetrician’s office, so what’s the difference? According to Dr. Carol Rumack, Professor of Radiology and Pediatrics at the University of Colorado, the difference may be much greater than you think.

What is an Ultrasound?

Believe it or not, the ultrasound did not start out as a medical tool at all. In fact, the ultrasound transducer (that wand that they pass over your stomach) was invented as a tool to locate submarines during World War II. The ultrasound would send out a sonar, or sound beam, which would bounce off a submarine and return to the source. Based on the timing of the beam’s return, the ultrasound would be able to calculate how far away the submarine was located and how big it was. Ironically, the ultrasound does the same thing with babies. The sound beam from the transducer bounces off of the baby and returns, and the computer puts together the information based on this phenomenon to figure out the shape, size, and location of the baby. In fact, today’s ultrasounds can give a relatively accurate picture of the baby’s form.

Down With Ultrasounds!

Some people actually swear off ultrasounds for all of pregnancy; others limit them to one or two per pregnancy. These people may draw a parallel between X-rays and ultrasounds. After all, for decades after the X-ray was discovered, doctors encouraged people to use X-rays for absolutely any purpose, and with virtually no precautions at all. Even when researchers finally discovered a link between cancer and X-rays, the public was stunned. How could X-rays not be safe?

Ultrasounds have not currently been linked to cancer or any other condition, but those wary of ultrasounds point out that not much research has been done on the subject. Why is this so? According to Dr. Rumack, ultrasounds are “not as risky as x-rays, so we don’t really have the manpower to go out there and investigate.” Although this has some people worried, Dr. Rumack maintains that the comparison is faulty, especially when ultrasounds are used correctly.

Possible Risks

So what are the possible risks of an ultrasound? There are two main suspects in the ultrasound controversy: heat and cavitation. Realize that fetuses can be sensitive to heat (hence the fact that pregnant women should not soak in a very hot bathtub), and that the sound energy released from the ultrasound transducer can raise the temperature of the fetus. This heat also causes cavitation, or the formation of bubbles in tissue, which some studies indicate may be detrimental to developing tissue.

Note that the only studies on the effects of heat and cavitation on human tissue have been done on a tissue culture, not on people, and that they involved very high levels of energy and a long heating period.

So should pregnant women avoid ultrasounds during pregnancy because of these risks? Dr. Rumack’s answer is adamant: they should not. “Doctors have not seen any proof regarding risks in a regular diagnostic ultrasound,” she maintains. “It’s obviously much safer than x-rays are. At the same time, it should only be given when medically needed—both because of the very small risks attached to it and because it is a waste of medical dollars when it is unnecessary.”

These risks, Rumack says, have almost nothing to do with a typical ultrasound. After all, ultrasound machines have an upper bound on the amount of energy that can be released, and this bound is set as low as reasonably possible. Experienced ultrasound techs are also trained to take certain safety precautions during the ultrasound process, such as using the ultrasound for only a limited amount of time and moving the transducer so that it does not rest for long in any one place.

Ultrasound Do’s and Don’ts

So should mothers-to-be be wary of ultrasounds? Not if they follow these guidelines:

In general, doctors should limit the number of ultrasounds in early pregnancy, due to the high number of cells and organs that are forming at that time. A single ultrasound in order to estimate the due date and test the heart rate is considered normal. In addition, ultrasounds based on maternal history (e.g. past miscarriages) may be necessary.

Avoid very long ultrasounds, such as those that take more than an hour, unless there is a specific medical reason why one would be necessary.

Visit a trained sonographer in an accredited lab whenever possible. Unlike those without much sonography training, they will know how to get the necessary pictures without holding the transmitter in place for too long, especially over the fetal heart. The machines will also be set at a safe output power and will be maintained well.

Allow vaginal probes when necessary. Contrary to popular belief, vaginal probes aren't any more dangerous than abdominal probes, and may in fact be less risky. “Because they’re closer, they can get a better picture without using a higher level of energy,” Dr. Rumack explains.

Don’t fear four-dimensional ultrasounds. Dr. Rumack reveals that these ultrasounds require a more complex computer, but don't send higher levels of energy into the fetus itself.

Ask for Doppler machines to be used much more sparingly than ultrasound machines. Dopplers visually show the heartbeat and can detect heart rate. Although there’s no proof that Dopplers are any more dangerous than ultrasounds, we do know that they do use much more energy. Obviously, Doppler machines can and should be used when the medical benefits outweigh the risks.

Don't dish out money for a fetal video or photograph. The technicians who will be performing the ultrasound aren't trained and are likely more interested in getting “the perfect shot” than in following standard protocol. “These people will frequently keep the ultrasound focused on the baby long enough to get lots of perfect pictures,” explains Dr. Rumack. “It is also exposing the patient to a potentially much higher level of energy without medical reason. Although we believe that ultrasounds are safe, there are plenty of things that we do that we feel are relatively safe, but that should not be done without a medical reason.”

In short, don't fret over medically necessary ultrasounds—but pass on shooting a fetal video or photo of your little one just for kicks. A trip to the sonographer is exciting, and if you play by the rules listed above, you can ensure both you and your baby stay safe.